linux shell 脚本个人规范总结

if 条件测试语句 then
    action
[elif 条件
    action
else
    action
]
fi

# a=5;if [[ a -gt 4 ]] ;then echo 'ok';fi; 
ok

#!/bin/sh
scores=40;
if [[ $scores -gt 90 ]]; then
    echo "very good!";
elif [[ $scores -gt 80 ]]; then
    echo "good!";
elif [[ $scores -gt 60 ]]; then
    echo "pass!";
else
    echo "no pass!";
fi;

1.for … in 语句
for 变量 in seq字符串；do
    action
done
说明：seq字符串 只要用空格字符分割，每次for…in 读取时候，就会按顺序将读到值，给前面的变量。

实例(testfor.sh)：（结果分行输出1，2，3，4，5，6，7，8，9，10）

#!/bin/sh
for i in $(seq 10); do
    echo $i;
done;

for i in python-devel readline-develsqlite-devel bzip2-devel openssl-devel ncurses-devel zlib-devel readline sqlite bzip2 openssl libdbi ncurseszlib;do
    result=`rpm -qa $i`
    if [ ! -n "$result" ]
    then
        yum -y install $i&>/dev/null
    else
        echo "--$i is install--"
    fi
done

filelist=`ls -l|awk {'print $9'}`
for file in $filelist
do
    if [ -f $file ]
    then
        echo "echo ${file}"
    fi
done

2.for((赋值；条件；运算语句))

for((赋值；条件；运算语句))；do
    action
done;

实例(testfor2.sh)：（结果分行输出1，2，3，4，5，6，7，8，9，10）
#!/bin/sh
for((i=1;i<=10;i++));do
    echo $i;
done;

while语句结构

while 条件语句；do
    action
done;

实例1:
#!/bin/sh
i=10;
while [[ $i -gt 5 ]];do
    echo $i;
    ((i--));
done;
运行结果：sh testwhile1.sh
10
9
8
7
6
实例2：(循环读取文件内容：)
#!/bin/sh
while read line;do
    echo $line;
done < /etc/hosts;

运行结果：sh testwhile2.sh
# Do not remove the following line, or various programs
# that require network functionality will fail.
127.0.0.1 centos6 localhost.localdomain localhost

语法结构：
until 条件；do
    action
done
意思是：直到满足条件，就退出。否则执行action.

实例(testuntil.sh)：
#!/bin/sh
a=10;
until [[ $a -lt 0 ]];do
    echo $a;
    ((a—));
done;
运行：sh testuntil.sh （分行输出 10 9 8 7 6 5 4 3 2 1 0 中的一个数字）

语法结构
case $arg in  
    pattern | sample) # arg in pattern or sample  
    ;;  
    pattern1) # arg in pattern1  
    ;;  
    *) #default  
    ;;  
esac 
说明：pattern1 是正则表达式,可以用下面字符：
                 *       任意字串
                 ?       任意字元
                 [abc]   a, b, 或c三字元其中之一
                 [a-n]   从a到n的任一字元
                 |       多重选择
实例：
#!/bin/sh 
case $1 in
start | begin)
    echo "start something"  
    ;;
stop | end)
    echo "stop something"  
    ;;
*)
    echo "Ignorant"  
    ;;
esac
运行：testcase.sh start
start something

语法：
select 变量name  in seq变量
do
    action
done
实例：
#!/bin/sh 
select ch in "begin" "end" "exit"
do
case $ch in
"begin")
    echo "start something"  
    ;;
"end")
    echo "stop something"  
    ;;
"exit")
    echo "exit"  
    break;
    ;;
*)
    echo "Ignorant"  
    ;;
esac
done;

sh testselect.sh
1) begin
2) end
3) exit
#? begin
Ignorant
#? 1
start something
#? 2
stop something
#? 3
exit 

使用方法：test EXPRESSION，如：
[root@localhost ~]# test 1 = 1 && echo 'ok'
ok
[root@localhost ~]# test -d /etc/ && echo 'ok' 
ok
[root@localhost ~]# test 1 -eq 1 && echo 'ok'
ok
[root@localhost ~]# if test 1 = 1 ; then echo 'ok'; fi
ok

[] 表达式

[root@localhost ~]# [ 1 -eq 1 ] && echo 'ok'           
ok

[root@localhost ~]# [ 2 < 1 ] && echo 'ok'                  
-bash: 2: No such file or directory

[root@localhost ~]# [ 2 < 1 ] && echo 'ok'

[root@localhost ~]# [ 2 -gt 1 -a 3 -lt 4 ] && echo 'ok'
ok    

[root@localhost ~]# [ 2 -gt 1 && 3 -lt 4 ] && echo 'ok'   
-bash: [: missing `]'

[[]] 表达式

[root@localhost ~]# [ 1 -eq 1 ] && echo 'ok'           
ok
[root@localhost ~]$ [[ 2 < 3 ]] && echo 'ok' 
ok
[root@localhost ~]$ [[ 2 < 3 && 4 > 5 ]] && echo 'ok' 
ok

# time (for m in {1..100000}; do test -d .;done;)
real    0m0.658s
user    0m0.558s
sys     0m0.100s

# time (for m in {1..100000}; do [ -d . ];done;)
real    0m0.609s
user    0m0.524s
sys     0m0.085s

# time (for m in {1..100000}; do [[ -d . ]];done;)
real    0m0.311s
user    0m0.275s
sys     0m0.036s